feat: add LLM-friendly docs and agent skill (#1679)

• feat: add LLM-friendly documentation and agent skill

Add llms.txt (concise overview) and llms-full.txt (full method reference) following the llmstxt.org standard, plus a cross-client Agent Skill (.agents/skills/) compatible with 30+ coding agents and a Claude Code plugin for marketplace distribution.

• generate_llms_txt.py: auto-generates both files by introspecting Client
• .agents/skills/python-binance/: agentskills.io-compatible skill
• python-binance-plugin/: Claude Code plugin wrapping the same skill
• README.rst: add LLM & AI Agent Support section with npx install command

• refactor: remove plugin, compact llms-full.txt

• Remove python-binance-plugin/ directory
• Switch llms-full.txt to compact format: one heading + description + params per method, no response examples (360KB -> 198KB)
• Drop RST-to-Markdown conversion code (no longer needed)
• Truncate long param descriptions to 80 chars

• refactor: slim llms-full.txt to ~18K tokens

Switch to compact one-line-per-method format with param names only. Truncate descriptions to 120 chars, drop auto-generated placeholder descriptions. Down from 48K to 18K tokens.

• fix: resolve all ruff and pyright errors

• client.py: fix extra space after keyword, spacing around colon
• helpers.py: add missing space after comma
• code-generator.py: fix operator spacing, indentation issues
• examples/depth_cache_threaded_example.py: fix indentation, add type ignores

• fix: ignore E203 in ruff config (conflicts with ruff-format slice style)